Ground GNSS Atmospheric Sensing - GNSS Remote Sensing: Theory, Methods and Applications - page 60

3.6 Summary

The ground IGS observation data can provide high temporal resolution zenith
tropospheric delay (ZTD). Together with global 3-hourly surface weather observa-
tions and 6-hourly NCEP/NCAR reanalysis products, water vapor can be obtained,
which can be used to investigate the water vapor climatology and variability. It
has been shown that the stronger water vapors are located in low latitudes, while
high latitudes have lower water vapor contents. The distinct season cycles are found
over all IGS stations. The marked seasonal cycles are in summer with a maximum
water vapor and in winter with a minimum water vapor. The higher amplitudes are
located in mid-latitudes with about 10-20 ˙ 0.5 mm and the lower amplitudes are
located in high latitudes and equatorial areas with about 5 ˙ 0.5 mm. The semi-
annual variation amplitudes are relatively weak with about 0.5 mm. The peak time
of semi-annual PWV variations are about in February-April and August-October.
In addition, significant diurnal variations of PWV are found over most IGS stations.
The diurnal (24 h) cycle has amplitude of 0.2-1.2 ˙ 0.1 mm, which is closely related
to the temperature, and the peak time is about from the noon to mid-night. The
semidiurnal (12 h) cycle is weaker, with amplitude of less than 0.3 mm.
With the development and increase of existing IGS stations and regional per-
manent GPS network, such as national Crustal Movement Observation Network of
China (CMONC) with about 30 continuous GPS sites, GPS Earth Observation NET-
work (GEONET) of Japan with about 1,000 continuous GPS sites, and Korean GPS
Network with about 80 continuous GPS sites, etc. it will provide denser GPS obser-
vations. Meanwhile, recent GPS radio occultation missions (e.g. CHAMP/GRACE,
Formosat-3/COSMIC, and TerraSAR-X) also provide high spatial global 3-D water
vapor estimations. In the near future, denser and near-real time atmospheric delay
and water vapor data can be achieved from all available continuous GPS and radio
occultation observations as well as other satellite observations, which provide new
chances for meteorology and atmospheric research.

References

Bevis M, Businger S, Herring TA, Rocken C, Anilies RA, Ware RH (1992) GPS meteorology:
remote sensing of atmospheric water vapor using the Global Positioning System. J Geophys
Res 97:15787-15801
Bevis M, Businger S, Chiswell S et al (1994) GPS meteorology: mapping Zenith Wet Delays onto
precipitable water. J Appl Meteorol 33:379-386
Boehm J, Schuh H (2004) Vienna mapping functions in VLBI analyses. Geophys Res Lett
31:L01603. doi : 10.1029/2003GL018984
Boehm J, Niell A, Tregoning P, Schuh H (2006) Global Mapping Function (GMF): a new empirical
mapping function based on numerical weather model data. Geophys Res Lett 33:L07304.
doi: 10.1029/2005GL025546
Chapman S, Lindzen RS (1970) Atmospheric tides: thermal and gravitational. Gordon and Breach,
New York, 200 pp
Dach R, Dietrich R (2000) Influence of the ocean loading effect on GPS derived precipitable water
vapor. Geophys Res Lett 27(18):2953-2956